"Malware authors move fast," Symantec's Stephen Doherty said in a blog post about digital pickpockets targeting Bitcoin, which was created two years ago.

"We have seen a recent Trojan in the wild targeting Bitcoin wallets" in computers running various versions of Windows, Doherty said.

"It has one motive: to locate your Bitcoin wallet.dat file and email it to the attacker," Doherty said. "This is not surprising considering the potential values in a Bitcoin wallet."

Bitcoins are digital currency that are accepted by a few online merchants. They can be traded at online currency exchanges such as Mtgox.com for real dollars.

Doherty said Bitcoin users should consider encrypting their wallet files.

"If you use Bitcoins, you have the option to encrypt your wallet and we recommend that you choose a strong password for this in the event that an attacker is attempting to brute-force your wallet open," he said.

Earlier this week, a Bitcoin user going by the handle of "allinvain" claimed on a public Bitcoin forum that his computer had been hacked and 25,000 Bitcoins worth $500,000 stolen.

Bitcoins have drawn the attention of members of the US Senate recently following a report that they have been used to purchase prescription drugs, cocaine, LSD and heroin at an online network called Silk Road.

Senator Joe Manchin, a Democrat from West Virginia, and Senator Charles Schumer, a Democrat from New York, wrote a letter to the US Attorney General and the Drug Enforcement Agency asking for the immediate shutdown of Silk Road.

"After purchasing Bitcoins through an exchange, a user can create an account on Silk Road and start purchasing illegal drugs from individuals around the world and have them delivered to their homes within days," they said.